As is well known to those skilled in the art, semiconductor chips must be tested for whether they are normal or not. Typically, a semiconductor chip is tested in such a way that test probes which are mounted to a test socket are brought into contact with the semiconductor chip and test current is applied to a test circuit board.
Of such devices for testing semiconductor chips, there is an anisotropic conductive sheet which can reduce damage to connection terminals (solder balls) of a semiconductor chip. In the anisotropic conductive sheet, conductive silicone parts are formed by vertically arranging metal balls (powder) in a main body made of silicone. Test current is applied through the conductive silicone parts to a test circuit board disposed under the main body, thus determining whether the semiconductor chip is normal.
To detect initial failure of a semiconductor chip, when the anisotropic conductive sheet is used as an electrical connection member of a test socket which is used in a heating test, a heat-cycle test, etc., if the anisotropic conductive sheet in which a positioning hole is formed in a resin film is used, electrodes of the anisotropic conductive sheet may be misaligned with respect to electrodes of an object to be tested because of thermal expansion of the resin film. As a result, stable and correct electric contact is not ensured, so that the reliability of the test deteriorates.
In an effort to overcome these problems, an anisotropic conductive sheet assembly was proposed in Korean Patent Laid-open Publication No. 2000-45941 which was entitled ‘Anisotropic conductive sheet with positioning means’.
In this conventional technique, the anisotropic conductive sheet assembly includes a positioning means for exactly positioning electrodes of the anisotropic conductive sheet with respect to circuit components having fine electrode pitches. When the anisotropic conductive sheet assembly is used as an electric connection member between the circuit components and a circuit board in a test or measurement of the circuit components or the circuit board, stable contact and reliable electric conduction can be ensured.
In detail, as shown in FIGS. 1 and 2, the anisotropic conductive sheet assembly of No. 2000-45941 includes an anisotropic conductive sheet 11 and a positioning metal plate 16. The anisotropic conductive sheet 11 includes conductive parts 12 which are provided in the anisotropic conductive sheet in thickness directions and are made of conductive material, and an insulation part 8 which is made of elastic insulation material and is formed in an area of the anisotropic conductive sheet outside of the conductive parts 12. The positioning metal plate 16 has positioning means 10 which is formed at predetermined positions around the anisotropic conductive sheet 11.
The anisotropic conductive sheet assembly having the above-mentioned construction is interposed between the circuit components and the circuit board and is pushed by a pressure fixing jig. Hereby, electric connection between the circuit components and the circuit board can be achieved.
Here, the positioning of the conductive parts 12 of the anisotropic conductive sheet 11 with respect both to the electrodes of the circuit components and to an electrode group of the circuit board can be realized by the positioning means 10, such as positioning holes or the like, of the positioning metal plate 16.
However, in the conventional technique, due to repeated tests, the upper and lower surfaces of the conductive parts 12 of the anisotropic conductive sheet 11 are damaged. Thus, the reliability of the test is reduced.
Meanwhile, another conventional technique was proposed in Korean Patent Application No. 10-2009-0017393 which was filed by the applicant of the present invention and entitled ‘Socket for testing semiconductor chips’.
As shown in FIGS. 3 and 4, the socket for testing semiconductor chips according to this conventional technique includes a support plate, a silicone base 10, a plurality of conductive silicone parts 20, a plurality of plungers 30 and a cap 80. The support plate has a planar shape. A coupling hole is vertically formed through the central portion of the support plate. The silicone base 10 is coupled to the coupling hole of the support plate. A boss 12 protrudes upwards from the silicone base 10. The conductive silicone parts 20 are formed in the boss 12 by arranging metal balls in vertical directions. The plungers 30 are seated on the conductive silicone parts 20 and come into contact with corresponding solder balls of the semiconductor chip. The cap 80 has insert holes 82 at positions corresponding to the plungers 30. A receiving space 86 is formed in the lower portion of the cap 80 so that the boss 12 is inserted into the receiving space 86. The cap 80 is coupled to the silicone base 10 to fasten the plungers 30 to the silicone base 10.
The upper ends of the plungers 30 come into contact with a device which is an object to be tested. A PCB (printed circuit board) is brought into contact with a lower surface of a lower piece of insulation tape which is attached to the lower surface of the support plate, so that the device is electrically connected to the PCB.
Furthermore, a lower protrusion 38 is provided under the lower end of a cylindrical body 32 of each plunger 30. Depressions 24 having semi-conical shapes are formed in an upper surface of a conductive silicone part 20. Thus, the lower protrusion 38 of each plunger 30 is seated into the corresponding depression 24, such that the plunger 30 can be stably coupled to the conductive silicone part 20, thus preventing the plunger 30 from being displaced from the correct position when the tests are repeated.
Furthermore, a cylindrical tip 39 protrudes downwards from the central portion of each lower protrusion 38. The cylindrical tip 39 is inserted into a receiving recess 26 which is formed in the corresponding depression 24, so that the plunger 30 can be disposed at the correct position.
In the technique of No. 10-2009-0017393, the contact efficiency between the socket and the device can be enhanced by installation of the plungers 30. However, foreign substances may be caught between the lower surfaces of the conductive silicone parts 20 and the PCB, with the result that contact resistance increases because of the foreign substances, thus reducing the reliability of the test.